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Main Colloquium |
Dr. Jaques Roland
| SCHEDULED |
Observatoire de Paris
Variations of the flux density of the nucleus of an extragalactic radio
source can be due either to the variations of the synchrotron spectra
of
the black holes contained in the nucleus, or to the ejection of VLBI
components. As a consequence of the variations of the synchrotron
spectra of the black holes, there will be periods during which the low
frequency and the high frequency observations will be aligned on the
same BH, say BH1, and periods during which the low frequency and the
high frequency observations will be aligned on different BHs, say BH1
and BH2. We obtained centroid position time series at 15 GHz from
MOJAVE
modelfitting giving epoch positions of the VLBI components and for each
epoch, we calculated the 15~GHz flux barycenter positions using a beam
$B = 2$ mas which corresponds to the $8$~GHz beam. The comparison of
the
$8$~GHz and $15$~GHz time series shows that: a) the time series are
generally correlated, but they can be anti-correlated during some
periods and b) the absolute position of the ICRF3 survey corresponds to
the mean position of the $15$~GHz flux density barycenter within $\leq
0.100$ mas$. The comparison of the $8$ and $15$~GHz has been done for
2201+315 which structure of the nucleus is known and for 0851+202 and
0923+392 which structures of the nucleus are not known.